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Analysis of the Keynesian Model
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來自 University of California, Irvine 的課程
宏观经济学的力量：真实世界中的经济学原理
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從本節課中
The Keynesian Model and Fiscal Policy
與講師見面
Dr. Peter NavarroProfessor
Paul Merage School of Business
[MUSIC]
Let's start our analysis of the Keynesian
model by looking at the aggregate production.
Aggregate production is defined as the total amount
of goods and services produced in the economy.
By definition such production creates an equal amount of income, so that
the aggregate production curve can be represented by a 45 degree line.
This is illustrated
in this figure, where production in dollars is represented on the vertical
axis. Real income or GDP is represented on the
horizontal axis, and the vertical line at Q superscript P represents
the economy's potential full employment income or GDP.
The upward-sloping, 45 degree line, representing the aggregate
production curve, means that at any
point along this curve, production equals income.
For example, at point A where the 45 degree line crosses the full
employment vertical line production and income both Q superscript P.
In contrast at point E. Both production and income are
at Q.
The economy's so-called recessionary gap is equal to
the difference between Q superscript P and Q.
In the Keynesian model, total spending or aggregate expenditures may be
represented algebraically by the equation that we first introduced in lesson one.
When we discussed the use of the flow of product or expenditures
method, to calculate income or gross domestic product.
Specifically aggregate expenditures AE equals consumption plus
investment plus government expenditures plus net exports.
And the aggregate expenditures curve is simply the vertical
summation of these four components. This figure
illustrates how these aggregate expenditures appear as
a curve in the basic Keynesian multiplier model.
In the figure, expenditures are measured on the vertical axis.
And real income, or GDP, is measured on the horizontal axis.
Note that the aggregate expenditures curve slopes upward.
But, has a flatter slope than the 45 degree line that represents
the aggregate production curve. Note also that the aggregate
expenditures curve, intersects the vertical axis at a level above zero.
Taken literally, this means that, even if income is zero,
people will still spend a certain amount of money on consumption.
Such expenditures are called autonomous
consumption, because they happen independently
of the level of income.
To fully understand how the Keynesian multiplier model works, we
not only have to understand the mystery of autonomous consumption.
We also have to understand why the aggregate
expenditures curve is flatter than the aggregate production curve.
The best way to do this is to
examine the major components of the Keynesian expenditure
function discussed above.
Consumption, investment, government expenditures and net exports.
The largest component of aggregate expenditures is consumption.
It accounts for almost 70% of total aggregate expenditures in the US economy.
This table divides consumption into three catagories.
Durable goods like autos and
household equipment.
Non durable goods like food and clothing,
and services like transportation and medical care.
Haynes sought to explain consumption expenditures in the following way.
First he posited that there is a level of consumption that will occur, even if a
person's income falls to zero. This zero income condition might
happen, for example, if a person loses his or her job.
Nonetheless, despite being unemployed, this person will still be
able to consume by dipping into his or her savings.
The level of consumption, that occurs regardless of
changes in one's income, is called Autonomous Consumption.
Second, Keynes said that there is a level of induced consumption,
that will depend on the individual's disposable income.
Where, disposable income is simply the amount of money
you have left after paying taxes to the government.
Now, Keynes further described this consumption behavior in
terms of a person's marginal propensity to consume.
Or, as it is also referred to as, the marginal propensity to expend.
This is simply the extra amount that people consume
when they receive an extra dollar of disposable income.
By the same token, there is a marginal
propensity to save, or marginal propensity to withdraw,
and it measures the extra amount people save
when they receive an extra dollar of disposable income.
Some people may
only spend 75 cents of every dollar
of their disposable income, and save 25 cents.
In this case, what will be the MPC, and what would be the MPS?
The MPC will be 0.75, while the MPS will be 0.25.
In another situation people may spend as much as
90 cents, and save only 10 cents of every dollar.
In this case, the MPC is 0.90 and the MPS is 0.10.
This figure illustrates that the marginal propensity
to consume, or MPC, equals the slope of the consumption function
and that the MPS is the slope of the savings function.
This is important to note because as we
shall soon see the aggregate expenditures curve is flatter
than the 45 degree line in the Keynesian
model precisely because the NPC is less than one.
Now let's turn to a discussion of
what the Keynesian consumption function actually looks like.
In fact it can be expressed in an equation, a table or a graph.
Algebraically we can represent the
Keynesian consumption function simply as follows.
Total consumption C equals autonomous
consumption C naught plus induced consumption.
Where induced consumption equals the marginal propensity
to consume, MPC, times disposable income, y sub d.
Typical example of such a consumption function is represented in this figure.
Note that this function intersects the vertical axis at
the level of autonomous consumption at $50 or point A.
While the slope
of the consumption function is simply the MPC or 0.75.
You can see now how this consumption function relates back to the
problem that Thomas Malthus originally identified
with Say's Law and the Classical model.
Namely that people won't necessarily spend everything they earn,
and aggregate expenditures therefore need not equal aggregate production.
